Strut supported cooled turbine blade



March 14, 1961 w. F. THOMPSON, JR 2,974,926

STRUT SUPPORTED COOLED TURBINE BLADE Filed April 8, 1959 INVENTOR. fiW/ n; F fiwapaapgfi BY mmyeak STRUT SUPPORTED COOLED TURBINE BLADE F. Thompson, In, Pittsburgh, Pa., assignonby mesue assignments, to the United States of America as represented by the Secretary of the Navy Filed Apr. 8, 1959, Ser. No. 805,107

1 Claim. (Cl. 25339.15)

This application relates to an improved air cooled rotating turbine blade of a type commonly known as a strut supported blade and to a method of making said blade.

In general, air cooled turbine blades are of two types, shell-supported and strut supported. The former type consists of relatively thick shelled hollow airfoil sections through which cooling air passes internally. The center cavity may be partially filled with inserts or baflles to improve cooling-air-to-blade heat transfer and to direct the air. The thick shell, however, is the only load carrying member.

On the other hand, the strut supported blades consist of relatively thin shells of airfoil wrapped around and supported by a thick, strong center strut. The cooling air passes between the thin shell and the center strut accomplishing some cooling of the shell and, in addition, cooling and insulating the strut.

Strut supported blades are considered superior to shell supported blades for high turbine inlet temperature applications because for any given cooling air flow the load carrying members of the strut blades will run cooler than the shell-supported blades. One of the chief problems involved in the use of strut-supported blades is mechanical design and manufacture.

Although a multitude of finned strut arrangements may be devised and manufactured with varying amounts of difiiculty, the chief problem with strut blades is to achieve a design which possesses the following desirable characteristics:

(1) A reasonable cooling air entrance cavity in the root,

(2) A sufiicient root-disk bearing area,

(3) A strong, un-notched connection between the center strut and the root bearing surfaces,

(4) An easy fabrication and assemblage.

An object of the present invention is to provide for the production of an improved strut supported blade which retains the cooling effectiveness associated with all strut supported blades, and in addition incorporates the desirable characteristics listed above.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understod by reference to the following detailed description which is considered in connection with the accompanying drawings wherein:

Figure 1 is a perspective view of the center strut and root combination with the outer shell removed.

Figure 2 is a perspective view of the blade shell and platform.

Figure 3 is a view along section line 3--3 of Figure 1 when the shell and shell platform of Figure 2 are mounted in place over the strut-root and fin assembly and the impeller is on the root platform placed in position.

Referring first to Figures 1 and 2 of the drawing, a blade 1 embodying the invention comprises the outer shell 3 and a center strut-root-fin assembly 5 adapted to conventional manner.

be assembled together in a manner which will be made more apparent hereinafter.

The root 7 of the strut-root-fin assembly, which is preferably of the conventional fir tree type, extends downwardly from the root platform 9 and is embedded in-the core of the turbine rotor preferably in the usual The strut 11, to which the fins 13 are attached in any suitable manner, is secured to and extends upwardly as shown from the root platform 9.

The ledge 15 which extends upwardly from the periphery of the root platform 9 may be made integral with the strut-root assembly, as is indicated in the preferred embodiment, or it may be fabricated separately and then welded or brazed to the platform. This ledge around the platform forms a plenum chamber 19 for the cooling air entering the beveled slot 21 in the root 7. As will be more apparent hereinafter, the cooling 'air is directed through the slot 21 to the chamber 19 by the impeller 23 which is secured as shown to the ledge.

The shell 3 (Fig. 2) of each blade 1 is fabricated separately in any suitable manner of thin, high temperature material with a platform 25 at the base similar in size to the root platform 9.

The shell may be formed in two sections. This may be accomplished either by forming the airfoil shell and platform separately of tubing and sheet and then brazing them together or by splitting the shell down leading and trailing edges and then forming each half integrally with half of the shell platform from sheet material.

In assembly the shell is slipped over the strut-root- 'fin assembly and spot welded at various places along the blade height to the strut fins 13 and at various places around the shell platform 25 to the root platform ledge 15. It was originally thought that the number of spot welds between the shell and the fins should be kept at a minimum to reduce heat transfer to the strut. However, tests have indicated that the persentage of contact area between shell and fins is unimportant for thin fins.

In operation, as the turbine rotor with its various radially secured blades rotates at high speed, air flows due to centrifugal action or by reason of the impeller 23 radially outwardly or upwardly (as seen in Fig. l) through each blade. continues on through the blade 1 between the center strut 11 and the shell 3 finally escaping from the blade preferably through a suitable aperture at the tip 27.

It has been found that the blade disclosed above provides for good contact between the strut and root, enables root and strut to be made in a single piece, permits more uniform transfer of load from the strut to all parts of the root lands, provides a generous air entry area through the root, insulates 'and cools the disk and maintains all the root lands and grooves intact.

While I have described my invention in detail in its present preferred embodiment, it will be obvious to Fthose skilled in the art, after understanding my invention, that various changes and modifications may be made therein without departing from the spirit or scope thereof. This method of construction can, of course, be used with various fin configurations on the strut and should not be construed as limited to the fin configuration illustrated.

I claim as my invention:

A strut supported turbine blade assembly comprising a tapered root member serrated along its apexed lower surfaces for engagement in the core of the turbine, said root member having upwardly extending edges whereby a ledge is formed about the periphery of the upper surface thereof, said root member also having a channel formed through a portion of the ledge; a sturdily constructed strut which is secured to the upper surface of the root member along a longitudinal portion thereof and The air enters the opening 21 and.

3 a extends upwardly therefrom; a plurality of fins secured substantially at right angles to the strut at spaced points therealong; a thin sheet metal casing which surrounds the strut and the fins and which is secured to said'fins at isolated points, said casing having a flang ed lower surface which is secured to the root ledge to form a plenum chamber therebetween; and means for conducting a cooling medium through the channel in the root member into said plenum chamber and upwardly between the strut and casing.

References Cited in the file of this patent UNITED STATES PATENTS Gerdan Feb. 18, 1958 Schum et al. Mar. 4, 1958 Wiese Feb. 17, 1959 FOREIGN PATENTS Great Britain July 15 1953 Germany Feb. 28, 1 955 

